This invention relates to marine seismic exploration and more particularly to a method for determining source and receiver statics.
A major problem in seismic exploration has been the estimation of time delays under source and receiver positions due to weathering, elevation, and shallow velocity changes. These time delays are often lumped together and simply called "static errors", and the corrections necessary to correct seismic traces for this error are called "static corrections" or "statics".
The widespread use of multiple coverage seismic profiling and the stacking of the multifold common depth point data as described in "Common Reflection Point Horizontal Data Stacking Techniques" by W. Harry Mayne, "Geophysics", Vol. XXVII, No. 6, Part 2 (Dec., 1961), pp. 927-938, requires the elimination of these static errors. Several methods are known for determining these static errors, one of which is described in "The Application and Limitations of Automatic Residual Static Correction Techniques" by B. M. Irving and J. K. Worley, presented at the 39th Annual International Meeting of the Society of Exploration Geophysicists in Calgary, Alberta, Canada. Such method, as well as others, provides a means of resolving the static estimates into source statics and receiver statics. It is these two components, source statics and receiver statics, which are utilized to correct the seismic data prior to common depth point stacking.
Some marine exploration areas are characterized by severe statics problems caused by the existence of a variety of subaqueous features and other sea floor irregularities. Such anomalies generally lie immediately below the water bottom and contain sediments having abnormally low velocities relative to normal sediments at shallow depths. They characteristically resemble channels ranging in depth up to a few hundred feet and lateral extent from a few hundred feet to thousands of feet. Velocities in these sediments are commonly less than half that of normal sediments. This decrease in velocity is due to gas bubbles in the sediment, causing a time delay in seismic energy waves traveling through such sediment relative to seismic energy waves traveling the same distance through normal sediments. One such marine exploration area is near the modern Mississippi River delta.